Field of the Invention
The present invention relates to an optical apparatus containing an image pickup apparatus, such as a film-based camera, a digital still camera, or a digital video camera. Particularly, the present invention relates to an optical apparatus equipped with a barrier mechanism that covers a lens openably and closably.
Description of the Related Art
Some digital still cameras have a barrier mechanism that covers a lens exposed to a subject side openably and closably on a lens barrel.
For example, a barrier mechanism in which barrier blades supported by a barrier ring rotate together with the barrier ring due to rotation of the barrier ring (revolution) and rotate with respect to the barrier ring (rotation) is proposed (see Japanese Laid-Open Patent Publication (Kokai) No. 2008-185728 (JP 2008-185728A)).
Moreover, a barrier mechanism that has a first barrier blade, a second barrier blade that overlaps with the first barrier blade in an optical axis direction, and a third barrier blade that does not overlap with the first and second barrier blades in the optical axis direction is proposed (see Japanese Laid-Open Patent Publication (Kokai) No. 2010-72060 (JP 2010-72060A)).
Furthermore, a barrier mechanism in which projections are formed on distal ends of a pair of barrier blades and depressions are formed on proximal ends of the barrier blades so that a projection of one blade corresponds to a depression of the other blade is proposed (see Japanese Laid-Open Patent Publication (Kokai) No. H5-27301 (JP H5-27301A)). In this proposal, when a pair of the barrier blades close, since a projection of one (the other) barrier blade fits in a depression of the other (one) barrier blade, surfaces of a pair of the barrier blades are arranged on the same plane. This causes a good closed state.
Moreover, a barrier mechanism that has a pair of main blades and a pair of auxiliary blades that open and close by following movements of the main blades that are opened and closed by a barrier driving means is proposed (see Japanese Laid-Open Patent Publication (Kokai) No. 2011-008140 (JP 2011-008140A)). In this proposal, a barrier closing interlocked part that is interlocked with a barrier closing interlocking part provided on the main blade is provided on the auxiliary blade, and a barrier disconnection prevention part in a U-shape that prevents disconnection between the barrier closing interlocking part and the barrier closing interlocked part is provided on the auxiliary blade.
Incidentally, when a barrier mechanism is provided corresponding to an outer shape of a lens, enlargement of an image circle and increasing of field angle enlarge an outer diameter of a lens barrel and also enlarge a size of a camera.
In this case, the outer diameter of the lens barrel decreases with respect to an opening part of the barrier mechanism by increasing the number of the barrier blades. However, if the number of the barrier blades is increased, it is necessary to increase an accuracy of a position of a bearing of a rotation shaft for the barrier blades so as not to generate a gap between the barrier blades in a closed state.
However, the mechanism of the above-mentioned JP 2008-185728A is disadvantageous to increase the accuracy of position of the bearing because the bearing of the rotation shaft for the barrier blades moves in a rotational direction of the barrier ring.
On the other hand, although the mechanism of the above-mentioned JP 2010-72060A does not move the bearing of the rotation shaft for the barrier blades, a gap that is not covered by the first and second barrier blades in the closed state is covered by a third barrier blade that is smaller than the first and second barrier blades. This is caused by increasing the number of barrier blades. Since the third barrier blade is driven independent of the first and second barrier blades, an energizing member is separately needed, which complicates the configuration and makes the assembly be troublesome.
A gap generated in the opening in the closed state of the barrier blades will be described with reference to FIG. 25. As shown in FIG. 25, an opening part 301a of a barrier cover 301 is formed in a rectangular shape, and the center of a rotation shaft 303 of a barrier blade 302 is arranged on the center line of the opening part 301a parallel to the long side of the opening part 301a. 
At the position where the barrier blade 302 rotates from an opened state by the minimum angle θ1 in a direction of an arrow A in the drawing so as to cover an upper right corner in FIG. 25 of the opening part 301a, an upper left part 301a1 of the opening part 301a is not covered, and a gap occurs. This is because the center of the circumscribed circle of the barrier blade 302 moves in directions of X1 and Y1 in the drawing when the barrier blade 302 rotates by the minimum angle θ1 around the shaft 303, the center of the circumscribed circle of the barrier blade 302 after the rotation shifts to the right side in the drawing.
Moreover, if the number of barrier blades is increased, the area of each barrier blade will decrease, and a barrier blade will become small relatively to the area of the opening part of the barrier driving ring. The opening part of the barrier driving ring needs a comparatively large opening area in order to allow an object light passing through a lens. Accordingly, if the barrier blade becomes small, the opening part of the barrier driving ring may become too large relatively, and the tip part of the barrier blade may not run on an end surface of the barrier driving ring in the closed state of the barrier blade. Accordingly, the tip part of the barrier blade cannot withstand static pressure received.